:root {
  color-scheme: light;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  --white: #fff; --ink: #181818; --secondary: #595959; --muted: #686868;
  --line: #e5e5e5; --surface: #f7f7f7; --hover: #f0f0f0;
  --space-1: 4px; --space-2: 8px; --space-3: 12px; --space-4: 16px;
  --space-5: 24px; --space-6: 32px; --space-7: 48px; --space-8: 64px; --space-9: 96px;
  --radius: 12px; --measure: 72rem;
}
* { box-sizing: border-box; }
html { background: var(--white); color: var(--ink); font-family: var(--font); line-height: 1.6; }
body { margin: 0; font-size: 1rem; }
a { color: inherit; text-underline-offset: 5px; }
button { font: inherit; color: inherit; cursor: pointer; }
:focus-visible { outline: 2px solid var(--ink); outline-offset: 5px; }
.skip { position: absolute; left: 24px; top: -100px; background: white; padding: 12px 24px; z-index: 2; }
.skip:focus { top: 12px; }
.shell { max-width: var(--measure); margin-inline: auto; padding-inline: 32px; }
.site-header { min-height: 112px; display: flex; align-items: center; justify-content: space-between; border-bottom: 1px solid var(--line); gap: 24px; }
.wordmark { text-decoration: none; font-size: 27px; font-weight: 650; letter-spacing: -1.2px; min-height: 44px; display: inline-flex; align-items: center; }
.header-note, .eyebrow, .meta, footer { color: var(--secondary); font-size: .8125rem; }
.header-note { letter-spacing: .02em; }
.intro { padding-block: 88px 72px; }
.eyebrow { margin: 0 0 20px; font-size: .6875rem; font-weight: 600; letter-spacing: .14em; text-transform: uppercase; }
h1, h2, h3, p { margin-top: 0; }
h1 { font-size: clamp(2.5rem, 5.4vw, 4.25rem); line-height: 1.12; letter-spacing: -.055em; font-weight: 550; margin-bottom: 24px; }
.intro p:last-child { color: var(--secondary); font-size: 1.125rem; margin-bottom: 0; }
.section-heading { display: flex; justify-content: space-between; align-items: baseline; gap: 24px; border-top: 1px solid var(--line); padding-top: 24px; margin-bottom: 32px; }
.section-heading h2 { font-size: 1rem; font-weight: 550; margin: 0; }
.section-heading p { margin: 0; }
.grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 48px 32px; padding: 0; margin: 0; list-style: none; }
.card { display: block; text-decoration: none; border-radius: var(--radius); }
.cover { aspect-ratio: 16 / 9; position: relative; border: 1px solid var(--line); border-radius: var(--radius); overflow: hidden; background: var(--surface); }
.cover img { display: block; width: 100%; height: 100%; object-fit: contain; }
.play { position: absolute; left: 16px; bottom: 16px; display: grid; place-items: center; width: 36px; height: 36px; border: 1px solid var(--line); border-radius: 50%; background: white; }
.play svg { width: 12px; height: 12px; margin-left: 2px; }
.duration { position: absolute; bottom: 16px; right: 16px; background: white; border: 1px solid var(--line); border-radius: 6px; font-size: .75rem; font-variant-numeric: tabular-nums; padding: 2px 8px; }
.card h3 { font-size: 1.1875rem; font-weight: 550; letter-spacing: -.025em; line-height: 1.4; margin: 20px 0 8px; }
.card p { color: var(--secondary); font-size: .9375rem; line-height: 1.6; margin: 0; max-width: 52ch; }
.card:hover h3 { text-decoration: underline; text-underline-offset: 5px; }
.card:hover .cover { border-color: #b0b0b0; }
.library-note { color: var(--muted); margin-block: 48px 0; font-size: .8125rem; }
footer { margin-top: 96px; padding-block: 24px 32px; border-top: 1px solid var(--line); display: flex; justify-content: space-between; gap: 24px; flex-wrap: wrap; }
footer p { margin: 0; }
.lesson { max-width: 960px; margin-inline: auto; }
.back { display: inline-flex; align-items: center; min-height: 44px; margin-block: 32px 24px; text-decoration: none; font-size: .875rem; color: var(--secondary); }
.back:hover { text-decoration: underline; }
.lesson-intro { max-width: 760px; padding-block: 8px 24px; }
.lesson-intro h1 { font-size: clamp(2rem, 4.5vw, 3rem); letter-spacing: -.045em; margin-bottom: 16px; }
.lesson-intro .description { font-size: 1.125rem; color: var(--secondary); max-width: 62ch; margin-bottom: 16px; }
.meta { display: flex; flex-wrap: wrap; gap: 8px 16px; }
.player { width: 100%; border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); overflow: hidden; }
video { display: block; width: 100%; height: auto; aspect-ratio: 16 / 9; object-fit: contain; }
.player-note { color: var(--secondary); font-size: .8125rem; margin-block: 12px 0; }
.player-note a { display: inline-block; min-height: 44px; padding-block: 8px; }
.error { padding: 24px; border-top: 1px solid var(--line); }
.error h2 { font-size: 1.125rem; margin-bottom: 8px; }
.error p { margin-bottom: 16px; }
.actions { display: flex; flex-wrap: wrap; gap: 12px; align-items: center; }
.button { min-height: 44px; border: 1px solid #b0b0b0; background: white; border-radius: 8px; padding: 8px 16px; text-decoration: none; display: inline-flex; align-items: center; }
.button:hover { background: var(--hover); }
.playback-status { font-size: .875rem; margin-block: 12px; }
.reading { max-width: 760px; margin-inline: auto; }
.reading section { margin-top: 48px; }
.reading h2 { font-size: 1.25rem; font-weight: 550; letter-spacing: -.025em; margin-bottom: 20px; }
.covers { padding-left: 20px; margin: 0; color: var(--secondary); }
.covers li { padding-left: 8px; margin-bottom: 12px; }
.takeaway { padding: 24px 28px; border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); }
.takeaway h2 { font-size: .75rem; letter-spacing: .08em; text-transform: uppercase; margin-bottom: 12px; }
.takeaway p { font-size: 1.25rem; line-height: 1.6; letter-spacing: -.015em; margin: 0; }
.transcript-intro { color: var(--secondary); }
.explanation { padding-block: 24px; border-top: 1px solid var(--line); }
.explanation h3 { font-size: 1rem; font-weight: 600; margin-bottom: 12px; }
.explanation time { display: inline-block; font-size: .75rem; font-weight: 400; font-variant-numeric: tabular-nums; color: var(--secondary); margin-right: 16px; }
.explanation p { color: var(--secondary); margin-bottom: 0; }
.formula { max-width: 100%; min-width: 0; overflow-x: auto; padding: 16px; margin-top: 20px; background: var(--surface); border-radius: 8px; font-size: 1rem; white-space: nowrap; }
figure { margin: 32px 0 0; }
figure img { display: block; width: 100%; height: auto; border: 1px solid var(--line); border-radius: var(--radius); }
figcaption { color: var(--secondary); font-size: .875rem; margin-top: 12px; }
main, section, article, li { min-width: 0; }
h1, h2, h3, p, a, li { overflow-wrap: anywhere; }
[hidden] { display: none !important; }
@media (max-width: 640px) {
  .shell { padding-inline: 24px; }
  .site-header { min-height: 88px; }
  .header-note { display: none; }
  .intro { padding-block: 56px 48px; }
  .intro p:last-child { font-size: 1rem; }
  .grid { grid-template-columns: minmax(0, 1fr); gap: 40px; }
  .section-heading { margin-bottom: 24px; }
  .card h3 { margin-top: 16px; }
  footer { margin-top: 64px; }
  .back { margin-block: 24px 16px; }
  .lesson-intro .description { font-size: 1rem; }
  .reading section { margin-top: 40px; }
  .takeaway { padding: 24px; }
  .takeaway p { font-size: 1.125rem; }
}
@media (prefers-reduced-motion: no-preference) {
  .cover { transition: border-color 160ms ease; }
}